Vertical silicon waveguide coupler bent by ion implantation

Curved GaAs cantilever waveguides for the vertical coupling to photonic integrated circuits

We report the nanofabrication and characterization of optical spot-size converter couplers based on curved GaAs cantilever waveguides. Using the stress mismatch between the GaAs substrate and deposited Cr-Ni-Au strips, single-mode waveguides can be bent out-of-plane in a controllable manner. A stable and vertical orientation of the out-coupler is achieved by locking the spot-size converter at a fixed 90 ∘ angle via short-range forces. The optical transmission is characterized as a function of temperature and polarization, resulting in a broad-band chip-to-fiber coupling extending over 150 nm wavelength bandwidth at cryogenic temperatures, with the lower bound for the coupling efficiency into the TE mode being 16±2% in the interval 900-1050 nm. The methods reported here are fully compatible with quantum photonic integrated circuit technology with quantum dot emitters, and open opportunities to design novel photonic devices with enhanced functionality.

27% slope efficiency in a WGM microcavity enabled by an Yb:YAG crystalline film

The choice of a laser gain medium is crucial in achieving efficient and high-power outputs of optically stimulated WGM microcavity lasers. This work employs an Yb:YAG crystalline film as the gain medium for the microdisk laser. The Yb:YAG crystalline film is exfoliated from a bulk of a Yb:YAG crystal by the ion-implantation-enhanced etching method. The crystalline film is shaped into a microdisk through focused ion beam milling. This Yb:YAG microdisk laser achieves a single-mode laser output (with a side-mode-suppression ratio of 27.8 dB) under a 946 nm laser pumping. The maximum slope efficiency reaches 27% with a maximum output power of 1.1 mW.

Efficient coupling between an integrated photonic waveguide and an optical fiber

Because on-chip integration of light sources cannot be realized effectively now, integrated nanophotonic chips must couple external light to the integrated photonic waveguide with high efficiency. Realizing high efficiency coupling requires a low-loss coupling structure. In this paper, the factors allowing high efficiency coupling to be realized are analyzed theoretically and the coupling between a lensed fiber and a tapered silicon nitride (Si₃N₄) waveguide is realized experimentally. Because the coupling efficiency of this structure is not ideal in the experiment, a scheme of direct alignment between the lensed fiber and a cantilever waveguide is proposed. Although the scheme offers a very high coupling efficiency in theory, because of the warpage of the waveguide they cannot be directly aligned experimentally. Finally, this paper advances a scheme for the tapered fiber to be directly overlapped onto the Si₃N₄/SiO₂ cantilever. It is found that the coupler maintains an ideal coupling efficiency for wavelength from 1530 nm to 1600 nm, laying a foundation for the integration of nano-photonic devices and optical fibers.

A Review of Recent Applications of Ion Beam Techniques on Nanomaterial Surface Modification: Design of Nanostructures and Energy Harvesting

Nanomaterials have gained plenty of research interest because of their excellent performance, which is derived from their small size and special structure. In practical applications, to acquire nanomaterials with high performance, many methods have been used to modulate the structure and components of materials. To date, ion beam techniques have extensively been applied for modulating the performance of various nanomaterials. Energetic ion beams can modulate the surface morphology and chemical components of nanomaterials. In addition, ion beam techniques have also been used to fabricate nanomaterials, including 2D materials, nanoparticles, and nanowires. Compared with conventional methods, ion beam techniques, including ion implantation, ion irradiation, and focused ion beam, are all pure physical processes; these processes do not introduce any impurities into the target materials. In addition, ion beam techniques exhibit high controllability and repeatability. Here, recent progress in ion beam techniques for nanomaterial surface modification is systematically summarized and existing challenges and potential solutions are presented.

Photonic-integrated circuits with non-planar topologies realized by 3D-printed waveguide overpasses

Complex photonic-integrated circuits (PIC) may have strongly non-planar topologies that require waveguide crossings (WGX) when realized in single-layer integration platforms. The number of WGX increases rapidly with the complexity of the circuit, in particular when it comes to highly interconnected optical switch topologies. Here, we present a concept for WGX-free PIC that relies on 3D-printed freeform waveguide overpasses (WOP). We experimentally demonstrate the viability of our approach using the example of a 4 × 4 switch-and-select (SAS) circuit realized on the silicon photonic platform. We further present a comprehensive graph-theoretical analysis of different n × n SAS circuit topologies. We find that for increasing port counts n of the SAS circuit, the number of WGX increases with n⁴, whereas the number of WOP increases only in proportion to n².

Silicon waveguide optical modulator driven by metal-insulator transition of vanadium dioxide cladding layer

We have fabricated compact optical modulators consisting of a Si waveguide with a VO₂ cladding layer. These devices showed a sharp decrease in transmittance at around 60 °C, which is attributable to the metal-insulator transition of the VO₂ cladding layer. By systematically varying the length of the device, we evaluated the transmission losses per unit length of the device to be 1.27 dB/µm, when the VO₂ cladding layer was in the insulating (ON) state and 4.55 dB/µm when it was in the metallic (OFF) state. Furthermore, we found that the device showed an additional loss in the OFF state, which is attributable to a structural effect. As a result, an 8-µm-long device showed a large extinction ratio of more than 33 dB.

Ion-beam-induced bending of semiconductor nanowires

The miniaturisation of technology increasingly requires the development of both new structures as well as novel techniques for their manufacture and modification. Semiconductor nanowires (NWs) are a prime example of this and as such have been the subject of intense scientific research for applications ranging from microelectronics to nano-electromechanical devices. Ion irradiation has long been a key processing step for semiconductors and the natural extension of this technique to the modification of semiconductor NWs has led to the discovery of ion beam-induced deformation effects. In this work, transmission electron microscopy with in situ ion bombardment has been used to directly observe the evolution of individual silicon and germanium NWs under irradiation. Silicon NWs were irradiated with either 6 keV neon ions or xenon ions at 5, 7 or 9.5 keV with a flux of 3 × 10¹³ ions cm^-2 s^-1. Germanium NWs were irradiated with 30 or 70 keV xenon ions with a flux of 10¹³ ions cm^-2 s^-1. These new results are combined with those reported in the literature in a systematic analysis using a custom implementation of the transport of ions in matter Monte Carlo computer code to facilitate a direct comparison with experimental results taking into account the wide range of experimental conditions. Across the various studies this has revealed underlying trends and forms the basis of a critical review of the various mechanisms which have been proposed to explain the deformation of semiconductor NWs under ion irradiation.

Broad-band surface optical coupler based on a SiO2-capped vertically curved silicon waveguide

A chip-surface optical coupler based on a vertically curved Si waveguide was demonstrated for coupling with high-numerical-aperture single-mode optical fibers with a mode-field diameter of 5 µm. This device features a dome-like SiO₂ coupler cap, which acts as collimation lens. We succeeded in fabricating this structure using an isotropic SiO₂ deposition technique employing plasma-enhanced chemical vapor deposition and obtained a light output that approximates that of a 5-µm-waist Gaussian beam. The fabricated coupler showed a coupling loss of less than 4.2 dB and a 0.5-dB-loss bandwidth above 150 nm for TE-polarized light.